Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Mike Poland, geophysicist with the U.S. Geological Survey and Scientist-in-Charge of the Yellowstone Volcano Observatory.

Sources/Usage: Public Domain. View Media Details

Yellowstone as a volcanic system may seem unique, with its history of huge explosive eruptions and lava flows. But did you know that there are similar caldera systems spread across the globe? And many of these are far more volcanically active than Yellowstone!

The United States is home to three large caldera systems that have erupted in the last 2 million years. Yellowstone is one, of course. Long Valley caldera, in eastern California near the town of Mammoth Lakes, is also well known. That caldera formed with a massive eruption 760,000 years ago, and numerous high-silica lava flows have subsequently erupted within and near the caldera. There is also a chain of silicic lava flows and domes that extends north from Long Valley, towards Mono Lake. The most recent eruption along this Mono-Inyo chain occurred about 250 years ago. Long Valley is very active seismically, in large part because the caldera sits atop faults that have caused uplift of the Sierra Nevada mountain range. The caldera also deforms, with more than 80 cm (30 in) of uplift measured since 1980. Some hot springs occur in the caldera, although not nearly at the same scale as at Yellowstone.

The third system is Valles caldera, located in northern New Mexico, near Los Alamos. That caldera formed due to large explosions 1.61 and 1.25 million years ago. Although Valles also experienced numerous lava flow eruptions after caldera formation, just like Yellowstone and Long Valley, it is not particularly active now. There is no significant seismicity and no ground deformation, and only one small hot spring. The most recent eruption occurred about 68,000 years ago.

There are many other caldera systems in the United States, although these are all much older and long extinct. The San Juan mountains of southern Colorado host numerous calderas that were active about 30 million years ago, and of course there is a trail of calderas caused by motion of the North American plate over the Yellowstone hotspot and since buried by younger lava flows, forming the eastern Snake River Plain over the past ~17 million years.

The USA is hardly alone in playing host to caldera systems, though. Calderas can be found in volcanic areas all around the world!

Sources/Usage: Public Domain. View Media Details

Nearly as famous as Yellowstone, Campi Flegrei caldera, near Naples, Italy, experienced violent explosive eruptions 39,000 years ago and also 15,000 years ago, although neither was anywhere near the size of the largest explosive eruptions from the Yellowstone system. On the other hand, Campi Flegrei, like Yellowstone, experiences frequent earthquake swarms and even outdoes Yellowstone when it comes to ground deformation, with several meters of uplift occurring over the last century. Campi Flegrei's most recent eruption formed the Monte Nuovo cinder cone in 1538.

The Greek island of Santorini is also part of a caldera, having experienced a large explosion about 3700 years ago—an eruption that might be the source of the myth of Atlantis. There were many subsequent lava flow eruptions, the most recent in 1950. During 2011–2012, uplift and seismicity at Santorini demonstrated that the caldera is far from extinct.

Another restless caldera can be found in Chile—the Laguna del Maule system. There have been at least three caldera-forming eruptions there in the past 1.5 million years, and numerous lava flows have occurred in the last 25,000 years. Uplift started at Laguna del Maule in the mid-2000s, reaching rates of up to 25 cm (10 in) per year!

In Japan, the Aira caldera, in southern Kyushu, formed about 30,000 years ago and is home to Sakurajima, which is one of Japan's most active volcanoes. Taal, in the Philippines, is a caldera system that erupted earlier this year, and Rabaul, in Papua New Guinea, has been persistently active since the 1990s. Indonesia hosts many caldera systems, the most famous of which is probably Toba, which experienced an epic eruption 76,000 years ago.

The Taupo caldera system, on the North Island of New Zealand, might be the most similar to Yellowstone, given the concentration of hot springs and geysers, as well as frequent seismic activity and deformation. Taupo's explosive eruption 26,500 years ago was larger than Yellowstone's big eruption 631,000 years ago, and Taupo's last significant eruption occurred about 1800 years ago.

We tend to think of Yellowstone as unique, and certainly it is with respect to the dense concentration of hot springs, geysers, and mud pots found there. In terms of volcanic style, however, there are many similar caldera systems around the world, some of which have had larger eruptions and some smaller, some of which are restless and some dormant. All have lessons to teach and are a focus of volcanologists around the world!